Blood glucose level measurements are commonly taken using portable measuring devices in what are called point-of-care applications i.e. applications in which the measurements are taken at the patient's bedside or in the patient's home. This type of measurement may be taken by an optical method implementing an enzymatic reaction leading to the formation of a coloured indicator, for example a reaction based on a tetrazolium salt. A blood sample is then placed between a light source and a photodetector, the latter measuring an intensity of the light transmitted by the sample. However, the haematocrit level in the blood may have an influence on the measurement. Specifically, blood particles, in particular red blood cells, scatter and/or absorb the light passing through the sample, and it is necessary to take into account this perturbation.
A first way of allowing for the effect of the particles is to carry out, prior to the measurement, a haemolysis. This is what is described in patent U.S. Pat. No. 5,866,349. In this patent, an optical method for determining the concentration of glucose in whole blood is described. After a haemolysis step, the method implements the aforementioned enzymatic reaction. However, the haemolysis step may have certain drawbacks: on the one hand, it is an additional step, requiring a lysis reagent be added and a time be waited for the amount of lysed particles to be sufficient. On the other hand, as indicated in patent application EP1875203, the particle lysis may release, into the blood plasma, intracellular components that are liable to react with the coloured indicator. Thus, the lysis step adds complexity and may have an impact on the precision of the measurement.
There are alternatives to haemolysis. For example, patent EP1875203 describes a device allowing an amount of glucose in a blood sample to be estimated without implementation of haemolysis. The measuring principle is also based on the formation of a coloured indicator via reduction of a tetrazolium salt. The blood sample is coupled to the photodetector by two lenses that are placed in succession between the sample and the photodetector. These lenses allow the signal collected by the photodetector to be increased. The photodetector may be a CCD photodetector matrix array. Two light sources are used, one emitting in a spectral band of absorption of the coloured indicator, the other emitting in the near infrared. The detection of the light radiation transmitted by the sample, illuminated in the infrared, allows a haematocrit level to be determined and the detection of the light radiation transmitted by the sample in the spectral band of absorption of the indicator allows an amount of glucose to be estimated, this estimation being corrected for the haematocrit level determined beforehand. However, the implementation of a complex optical system based on two hemispherical lenses negatively affects the compactness of the device and its cost.
More generally, apart from blood, the analysis of a liquid containing particles may pose problems related to the presence of said particles. Known methods employ centrifugation of the sample to achieve an effective separation of the particles. However, centrifugation is a technique that is not easily integrable into a point-of-care type device. It requires the use of moving parts and powerful actuators. It may also lead to a lysis of certain particles.
The proposed invention addresses this problem, by providing a simple method allowing a characterization of a liquid containing particles to be obtained. The invention may be implemented using a simple and inexpensive device requiring neither a complex optical system nor successive illumination of the sample at two different wavelengths.